Like Aristotle, Kant believed that knowledge begins with experience, or what he calls practical reason. Moral principles can be understood by studying human experience: reality can tell us how things ought to be. Like Plato, Kant defines human nature in terms of reason and the freedom that reason makes possible. Because of this definition of human nature, Kant resisted Aristotle’s prescriptive definition of what it means to be fulfilled and the detailed laws which hinge on that definition. He saw that if human beings are presented with a list of laws, this actually limits the freedom which is a distinctive part of their nature and makes the exercise of reason unnecessary. To be a fulfilled human being is to be a free, rational human being, not to follow lists of laws mindlessly, fit in with convention and take the easiest route through life.

Allowing people their own choices

For Kant the role of the moral philosopher must be to help people to reason out the principles which they should follow and then to choose to follow those principles freely, not to tell people what to do specifically. Think about it – is the better teacher the one who enables students to do things themselves so they are capable when teachers are no longer around, or the one who just gives the students the answers to fill in on the exam papers? Aristotle’s approach to moral philosophy could be seen as almost controlling, undermining the essential roles of reason and freedom and preventing people from finding the fulfilment he wants them to find. For Kant the role of the moral philosopher is difficult, similar to the role of a good teacher or a good parent. It involves helping people only at a distance, allowing them to make their own decisions and accepting the risk that they might make a mistake, even in the knowledge that that mistake might be catastrophic and irreversible.

Think about learning to drive, or teaching somebody to drive. How hard is it to allow an inexperienced teenager to take the wheel for themselves, risking the health and lives of numbers of people in the process? When does the good instructor allow the learner driver to go solo?

a. On the first lesson, to see what happens?
b. After a good grounding in theory and some sessions in a car park?
c. Never – it is safer that way?

Kant's categorical imperative

The moral philosopher can suggest the basic principles which might guide rational, free decisions. For Kant all free, moral decisions should be guided by the categorical imperative, a single simple principle derived from human experience, which, it seems, really does command all free, rational beings. This principle is, however, all too easy to describe in ways that can be misunderstood and misapplied, wilfully or otherwise. In the Groundwork for the Metaphysics of Morals (1785), Kant put forward more than six wordings of the principle, which can be explained in terms of three different ways of describing it. It is important to remember that Kant never intended these wordings to be considered, let alone applied, separately. He believed that they were ways of gesturing towards the same essential law, not a law which he had invented or which could be formulated and applied mindlessly. He believed they together made up a command which is inherent in the nature of human beings but which resists being codified because doing so would remove that which is also inherent in human nature – freedom.

Seeing others as lesser or equal

In other words Kant asks people to consider what would happen if everybody’s actions set a precedent for others to copy. What would happen if some people through their actions use people as a means to an end, effectively assuming that some people are worth less than others, even nothing at all? It is irrational to think that we can allow some people to do things which others are not allowed to do, that doing something will not give others licence to do the same and that equals should be treated as more, or less, important than each other. Reason dictates that humanity must be respected for itself, that selfish urges or emotional preferences must come second to a basic respect for human life. Reason dictates that we must act fairly, consistently, according to principle and not unjustly, instinctively or without sense.

When expressed like this Kant’s moral philosophy ceases to seem so complicated and alien. The American philosopher Allen Wood pointed out that many people's reaction to Kant’s ethics resembles an allergic reaction: they reject Kant really without rational consideration and argument. He goes on to speculate that this might be because most people, particularly in the English-speaking world, first engage with Kant through the Groundwork. The Groundwork is short, but it is not an easy work to begin a study of Kant with. Many short works conceal difficult core theses – think about Animal Farm, which is not a simple introduction to Orwell; Jude the Obscure is shorter than many of Hardy’s great novels but it is certainly not easier, the poems of William Blake, ee cummings and RS Thomas are often short, but their apparent simplicity is misleading.

MacIntyre's criticism

Alistair MacIntyre, in his 1985 book After Virtue, accuses Kant of being action-centred rather than agent-centred, of being too worried about the rights and wrongs of little things and not worried enough about people's broader moral character. We all know that someone can seem bad despite keeping the law and that another can seem good despite having done something bad. Who was better, Anne Frank’s neighbours who, like good citizens, turned the family over to the Gestapo, or Dietrich Bonhoeffer, who risked everything in an assassination attempt on Hitler?

In fact, the broader virtue ethic that MacIntyre proposes is based on the ethic that Kant developed through the Metaphysics of morals (1797), the Critique of Judgement (1790) and the essay Towards perpetual peace (1795). As was said earler, the Groundwork was just intended to get people asking the right questions. Kant had no easy answers to what we should do with our lives; in his view it is for every individual to use their reason and their freedom to work out how to be good for themselves by reflecting on their experience of other people’s lives. He accepted that mistakes are bound to be made, and that regret would temper the satisfaction of even the best person, yet he never despaired of the possibility of human beings living up to their natures and being good. He was never obsessed with rules in the way that MacIntyre suggests; the Groundwork, which MacIntyre uses to support this view, aims to work out how a virtuous person would act, not to railroad anyone into following a code first and being human second.

Character as the sum of a person's choices

One important point to take from Kant into the discussion of virtue ethics is that the general moral character is built up of every choice it has made. Modern virtue ethics tend to shy away from offering definite advice about right and wrong and are unclear about the virtues we should aspire to; in the confusion it would be easy to justify most behaviour. Kant is clearer and more demanding, not afraid to pin down his virtues of rationality and freedom or to describe how they would be enacted.

The Groundwork for the metaphysics of morals was produced to elicit discussion and controversy related to themes which Kant was handling at more length in the Metaphysics of morals and the Critique of practical reason. Kant often produced essays or short works whilst he was working up major books, so that many of the issues with and criticisms of his ideas would be flushed out whilst he still had time to respond to them. Unfortunately, Kant’s major books became so long and complicated as a result that many people never got as far as to read them, relying instead on the shorter works.

The Groundwork begins by arguing that the only inherently good thing is a good will. What does Kant mean by this? Kant uses two German words for "will", Wille, which refers to the universal principles of reason, and Willkur, which is the moral character within every one of us. Human nature, our character, is to be rational, but also to be free, therefore the Willkur is not programmed to follow the Wille, but must choose to do so. When faced with a moral decision the Willkur has to weigh up the apparently competing desires of the animal self (the Bestimmung), of the social/emotional self, and of reason, and freely choose to follow reason, subordinating the emotions and instincts to it. Only when somebody freely chooses to follow reason are they good and only that character which has always freely chosen the rational is truly good and deserving of any metaphysical reward that there may be.

Truly free actions

This is the beginning of a problem for Kant. Who among us can claim to have always acted freely? Never to have acted out of habit, fear, thoughtlessness? Who among us can claim to have always acted rationally? Never to have followed baser instincts, to have been selfish, to have preferred friend or family member, to have done something bad on the basis that nobody would ever know, to have done something of which we are ashamed? Obviously, particularly given the typical behaviour of childhood [check], nobody can measure up to the standard of goodness that Kant describes, that of a moral character which has always freely chosen what is rational for its own sake, and therefore everybody is imperfect to some extent. This does not seem problematic, it seems true to human experience, so why is it a problem for Kant?

The problem lies in the irrationality of asking people to do, or to try to do, something which we all know that they cannot achieve. Why try to be good when you know that you can’t? It can’t be for the immediate rewards of good actions – because there often aren’t any. Kant’s broader worldview depends on the assumption that things are ordered, predictable, fair. What we experience is how things are and the universe is indeed governed by rational laws as it seems to be. In order to explain why the universe is fair, to suggest why things are ordered and rational and to account for bad things happening to good people, Kant had to suppose the existence of God and an afterlife. Kant could not account for why a good God would reward bad people by allowing them into heaven and yet there could be no other reward for the good actions that bad people do, so why should bad people try to overcome their shortcomings and try to be good? If there is no reason for any of us to make a moral effort, what is the point? The universe is not fair if everybody in it is condemned for not doing something that they cannot do. If the universe is not fair in this, then what reason is there to suppose that it is free in other ways, that what we experience really is how things are and that anything really is predictable?

Kant's view of Jesus Christ

Kant never satisfactorily extricated his philosophy from this problem of what he called "radical evil" although he (surprisingly for some people) argued for the need for God and particularly Christ, the proof that it is possible to be good (despite all appearances to the contrary) and that the world is indeed ordered and fair as Kant assumes it must be. For Kant, Jesus' example shows that human beings are able to overcome radical evil and fulfil all their potential to be rational and free, enacting the categorical imperative in every moral action and not being influenced by selfish impulses or the fear of pain and death. The effects of Jesus' life show, for Kant, the effects of people choosing the good for its own sake in building a better world, the summum bonum, which Kant uses as a justification for calling on individuals to do good without hope of personal reward. Kant does not focus on the identity of Jesus; it is sufficient that he is fully human and fully good and as such is a sign from God that salvation is possible and things will come right in the end. In Kant's view Jesus existed through the grace of God and believing in him enables us to be good as God wills us to be. Unsurprisingly this was not sufficiently close to orthodox Lutheran doctrine for Kant's book Religion within the bounds of reason alone (1793) to be acceptable to the church authorities at the time.

Building a better world

However one of Kant’s suggestions went on to inspire philosophers to take his ideas in a new direction. In his essay Towards perpetual peace Kant suggested that the reward for good behaviour would not be for individuals but would come in the effects of improving society, in the satisfaction every one of us would have in knowing that in every promise kept and every truth told we had done our bit in building a better world. A generation of philosophers took this idea and ran with it, developing systems from Mill’s utilitarianism to Marx’s communism – ways of defining and prescribing the good without bringing God into the discussion.

Some people suggest that the value Kant placed on reason as the defining feature of human nature would have made him unlikely to see those with no or less rational potential as fully human. Indeed this quote from the Groundwork seems to confirm this view of Kant – at least for those who read no further: ‘‘Now I say that … every rational being, exists as an end in himself and not merely as a means to be arbitrarily used by this or that will … [B]eings … if they are not rational [have] only a relative value as means and are therefore called things" (8:428).

This might mean that Kant would accept the euthanasia of people who are brain-damaged or mentally disabled – even of criminals. Certainly, some Nazis interpreted Kant’s writings in this way. In his early years this criticism would have been true – Kant, as a man typical of his age thought that women and members of other races were less rational and thus only to be treated as human out of charity – but his understanding of human value changed when he read the writings of the Swiss philosopher and novelist Rousseau (the only time when Kant interrupted his daily walk was when his copy of Rousseau's treatise on eduction Emile arrived). He wrote to a friend, "there was a time when I believed that [reason] constituted the honour of humanity, and I despised the people who knew nothing. Rousseau set me right about this. This blinding prejudice disappeared. I learned to honour human beings" (quoted in Allen Wood's Kant’s Ethical Thought, page 5).